The definition of your structure is made through Attributes that store part of the information that concerns the structure.
Examples of attributes are: customer name, product id, and product price
How to create an Attribute:
In the eSpace tree, under the Data layer, right-click on the structure in the Structures folder.
When you delete an attribute, Service Studio is permissive, i.e. no test is done to check whether the attribute is being used. However, eSpace validation detects this and returns an error. The eSpace is not valid and you must fix the elements where the attribute is being used.
Structure Attributes Properties | Structure Definition